The recent hadron therapy techniques for treating cancer make it possible to deliver a dose precisely on a target volume, for example a tumor, while preserving the surrounding tissue. Such a hadron therapy installation comprises a particle accelerator producing a charged particle beam, means for transporting the beam, and an irradiating unit. The irradiating unit delivers a dose distribution on the target volume and generally comprises means for monitoring the delivered dose, for example such as an ionizing chamber, as well as monitoring means for the beam, for example such as a collimator or scanning magnets based on the delivery mode of the beam used.
Most hadron therapy installations comprise a rotary gantry supporting a system for delivering the beam comprising a beam transport line ending with an irradiation unit, which my als be called a beam outlet unit. The rotary gantry is capable of rotating 360° around a horizontal axis of rotation, such that the irradiation unit can deliver a treatment beam from several irradiation angles. In the more compact recent hadron therapy installations, the irradiation unit may only rotate by an angle smaller than 360° around a horizontal axis of rotation.
Often, hadron therapy treatment occurs over several sessions. The patient must be positioned correctly before each treatment session. The position of the target volume to be treated is generally determined relative to a reference point situated in the patient's body. This determination is made using an imaging device, for example such as a PET scan. The patient is then positioned so that the target line to be treated coincides with a point of the treatment space called the isocenter. The isocenter is defined as a point in space at the intersection between the horizontal axis of rotation of the gantry and the central axis of the beam delivered by the irradiation unit at multiple incline angles of the gantry. In practice, all of the central beam axes delivered at several incline angles of the gantry do not intersect at a single point, but each intercept a small spherical or ellipsoid volume. The center of mass of said spherical or ellipsoid volume is generally defined as the isocenter of the rotary gantry. This isocenter is for example determined using the method described in document U.S. Pat. No. 7,349,523 or the method described in document EP2186542.
The patient must be positioned precisely relative to said isocenter. The patient is first pre-positioned using positioning means capable of locating reference point situated in or on the patient's body. For example, references are marked on the patient's skin so as to coincide with those of the laser beam. A second means may be an x-ray source and a detection panel positioned in a stationary manner on either side of the patient in the treatment area, so as to view references comprised in the bone structure of the patient or markers pre-inserted into the target volume to be treated and visible by x-ray imaging.
In order to allow more precise positioning of the patient, an imaging device using cone beam computed tomography, commonly called CBCT, is used. Such a device comprises equipment for producing x-rays and equipment for receiving x-rays, which can be positioned on either side of the patient and pivoted around the patient, so as to take a plurality of images designed to be processed by a computer to reconstruct a three-dimensional image of the inside of the patient's body. The obtained three-dimensional image makes it possible to view both the bone structure and the soft tissues. The therapist may also adjust the position of the patient more finely.
Document EP2243515 describes a hadron therapy installation comprising an x-ray device for emitting x-rays toward the target volume. This x-ray producing equipment is integrated into a nozzle providing the target volume with the beam of charged particles. It can pivot, inside said nozzle, between a first position, in which is arranged in the trajectory of the charged particle beam, and a second position, in which it is arranged outside the trajectory of the charged particle beam. X-ray receiving equipment is mounted across from the nozzle relative to the patient, and forms an optical alignment with the x-ray source when the x-ray producing equipment is in the first position.
Other installations comprising a similar imaging device are described in document EP1454653 and WO9818523. These three imaging devices are provided to perform “beam eye view” simulations, so as to verify that the orientation of the target volume to be treated coincides with the field of the treatment beam. In these imaging devices, the x-ray receiving equipment must be able to rotate synchronized with the x-ray producing equipment, so as to be able to form the optical alignment with the x-ray source. A device allowing the movement of the x-ray receiving equipment synchronously with the x-ray producing equipment must advantageously be relatively compact, so as to facilitate access to the patient. Such a device must not collide with the enclosure surrounding the treatment area, or with the support arms of the patient's bad.
Other imaging devices intended for the positioning of the patient in a hadron therapy installation are described in document US20080219407 and US20090065717. These imaging devices comprise x-ray producing equipment and x-ray receiving equipment mounted on a rotary arm in the shape of an arc of circle. These imaging devices have the drawback of cluttering the treatment area. Furthermore, collisions between the arms supporting the x-ray producing and receiving devices and the irradiation unit may occur.
Another imaging device is described in document WO2006060886 and comprises a rotary structure fastened on a vertical wall forming the bottom of the treatment area. The rotary structure is provided with:
a first telescoping or folding arm, which in turn is provided with x-ray producing equipment; and
a second telescoping or folding arm, which in turn is provided with x-ray receiving equipment.
The rotary structure is configured to pivot around the patient with the arms extended or unfolded depending on the embodiment of the arms, while the rotary gantry of the hadron therapy installation is immobilized. This device requires means for monitoring the rotation of the rotary structure to avoid collisions with the irradiation unit. Although the bulk is reduced relative to CBCT devices mounted on rotary arms in the shape of an arc of circle, it would be advantageous to reduce this bulk even more and facilitate access to the patient, in particular when the arms are extended or unfolded.
Document WO2010076270 describes a hadron therapy installation comprising a rotary gantry supporting a beam transport line ending with an irradiation unit capable of delivering a treatment beam. The installation also comprises a moving floor that can be driven by the rotation of the gantry. According to one embodiment as described in this document, the installation comprises a cone beam computed tomography device comprising an x-ray source and x-ray receiving equipment. The x-ray source is positioned on a telescoping arm connected to the rotary gantry, so as to deliver a conical beam whereof the central axis is orthogonal to the central axis of the treatment beam. The x-ray receiving equipment can either be attached on an arm connected to a vertical wall forming the bottom of the treatment area and capable of rotating with the gantry, or on a rotary structure positioned outside the treatment area. The position of the x-ray source requires the presence of an opening in the moving floor to allow the x-ray beam to pass through the moving floor. Furthermore, the rotation of the x-ray receiving equipment must be perfectly synchronized with the rotation of the gantry, so as to preserve the alignment of the x-ray source with the isocenter and the x-ray receiving equipment.
It is desirable to position an integrated imaging device in a hadron therapy installation. This imaging device must advantageously be relatively compact, more particularly during installation and positioning of the patient by the therapist. Such an imaging device should be able to be used to carry out a cone beam computed tomography and fluoroscopy method. It is also desirable for the imaging device to be able to be integrated into a hadron therapy installation, for example comprising a moving floor whereof one portion is planar and aligned with the floor of the treatment room, as described in applications WO2010076270 or in the Belgian or US patent application filed that same day by the applicant, both incorporated by reference.